Not Applicable.
This invention relates in general to epicyclic drives and, more particularly, to an epicyclic drive with unified planet assemblies and to the planet assemblies themselves.
In an epicyclic or planetary drive, the planet gears rotate in a carrier which itself may or may not rotate. Typically, the carrier is of the straddle-mounted variety in which pins extend between two carrier plates, and the planet gears rotate on antifriction bearings carried by the pins. Sometimes each bearing contains two rows of rolling elements, such as tapered rollers or balls, with the rolling elements of the one row being mounted in opposition to the rolling elements of the other row. This enables the bearing for a planet gear to transfer axial loads in both directions, as well as radial loads, between the gear and its pin. The presence of antifriction bearings brings with it demands for a considerable amount of precision. In the first place, the gears must be machined to within close tolerances to receive the outer races of the bearings and the same holds true for the pins over which the inner races fit. During the assembly of an epicyclic gear system the builder must insure that the bearings are adjusted properly. If the bearings are set with too much preload they may fail prematurely. On the other hand, too much end play in the bearings leaves the bearings with excessive internal clearances, and the gear may tilt on its axis and misalign with the sun and ring gears. This produces greater noise and wear in the gears.
The gears of an epicyclic drive require lubrication and so do the bearings on which the planet gears rotate. A low level of oil in the gear case may suffice to provide lubrication for the gears, but a higher level of oil is generally required to lubricate the bearings for the planet gears, inasmuch as they usually operate in an elevated position in the case. Even when the oil level is high enough to supply lubricant to the exterior of the bearings for the planet gears, this does not insure that the oil will enter the bearings and lubricate the raceways and rolling elements. Indeed, it is often necessary to make provision for introducing oilxe2x80x94a second oil supplyxe2x80x94into the space between the two rows of rolling elements on which each planet gear rotates. The phenomenon is particularly troublesome during high-speed operation in which oil is flung away from the bearings by the spinning gear faces and carrier or in which oil is naturally pumped centrifugally away from the bearing centers as a consequence of the bearing geometry.
Moreover, since a considerable amount of oil is exposed to the gear teeth, the oil tends to churn. The churning reduces the effective operating oil level and this reduces the availability of lubrication to the bearings. Raising the oil level to accommodate the bearings only increases the churning. The temperature of the oil increases with churning and the capacity of the oil to lubricate lessens. This may lead to pitting in the gear teeth.
The present invention resides in a planet assembly including a planet gear, a pin extended through the planet gear, and a bearing located between pin and gear. The invention also resides in an epicyclic drive including a carrier in which the planet assembly is installed. The pin may be of a one or a two piece-type assembly. The invention further resides in a process for assembling the planet assemblies.
The foregoing and other objects, features, and advantages of the invention as well as presently preferred embodiments thereof will become more apparent from the reading of the following description in connection with the accompanying drawings.